Modern two-piece containers, such as aluminum beverage containers, having an integrated sidewall/bottom and a separate top are formed, in part, by large ram/die bodymakers. Briefly, the bodymaker receives a shallow, cup-like container blank having a larger diameter and thickness than the container body to be formed, and a reciprocating ram forces the blank through a series of drawing and ironing dies within a tool pack to reduce the diameter of the blank and thin and lengthen the sidewall. As a final step, the ram forces the just-formed container body against a domer to produce the bottom dome geometry of the container. The ram retracts and the container body is removed from the bodymaker and transported to other apparatus for necking, coating and other finishing operations.
The first die in the tool pack is a redraw die which, through a method of cold working, substantially reduces the diameter of the container blank, lengthens the sidewall and begins the sidewall thinning process. After the blank enters the bodymaker, it is held against the front surface of the redraw die by a reciprocating, cylindrical redraw sleeve. The nose of the ram then passes through the redraw sleeve and forces the container blank through the redraw die and then through the other dies, after which the redraw sleeve and ram retract and the container body is removed.
Typically, both the ram and the redraw sleeve are mechanically driven off of a rotating wheel through a series of crankshafts, arms and linkages. To provide the necessary timed, linear motion to the redraw sleeve, and to adequately hold the redraw sleeve against the redraw die during drawing and ironing operations, an eccentric, mechanical cam assembly is interconnected to the bodymaker drive wheel with an actuating rod coupled between the cam assembly and redraw sleeve. To retract the redraw sleeve a mechanism such as a hydraulic spring or air cylinder is employed. A counterbalance mechanism is also generally used to provide substantially uniform force by the redraw sleeve against the container blank to ensure appropriate metal flow of the container blank between the redraw sleeve and the redraw die.
As noted above, a typical bodymaker employs a single mechanical assembly to provide both the reciprocal motion to the redraw sleeve and the holding force. Such an assembly is extremely bulky and requires substantial force to set it into motion at the appropriate times and to bring it to a halt. For example, the force required to move the redraw sleeve approximately two and one-half inches from the retracted position into the extended position is substantial (i.e., substantially greater than 600 pounds), and the force utilized to hold the redraw sleeve in place against the container blank is normally about 1,500 pounds. More significantly, the components of mechanical assemblies are prone to rapid wear and frequent breakdown, necessitating down time for maintenance and repair. In fact, at the present time, parts and labor alone for a single bodymaker may cost over $15,000 per year. Lost production capacity when machines are down adds further significant cost.